Electrical switch



Jan 3, 195@ B. R. CRISWELL ELECTRICAL SWITCH Filed OC'b. 3, 1946 BYRON R CR/swELL v INVENTOR.

H/s A TTORNEY Patented Jan. 3, 1950 emomiiifiii gwmon nyron n. criswelr nake Forest, lll assiglior to "Zenith Radio Corporation, a corporati'on of Illinois Application 'october s, 194s,seriaiNofvooms 3 Glaims. 1 This i invention relates to tone control arrangements of the type'particularly useiul'in Small portable "apparatus; such as wearable radios or hearing aids. In such'sman portable apparatus it is advantageous to minimize the number of "eontrols to allow for ease ofop'eration.

brie 'wayin 'which- -the number of contnols can be minimized is by having a single control serve thepurpo'se 'of two-controls; This a'dva'nta'gein controls should be obtained by u'si ng-as ffe w electiic'al and mechanical elements-aspos'sible and theresulting "combination of controls should-be no more'complex or diflicult to fabricateend assemble than iftwo separatecontrols are used. *It' isfither'eiore, an object of the present invention to provide an improved 'tone control in coinbinationwith an on-off controlwhich-is simple and inexpensive'to manufacture, readily operable by the user and which doesnot-a'dd materially to 'tlie weight or bulkiness of the apparatus with which it c'o-acts to switch -"onor oil-and to pro- 'diicediliernt characters-'oftone.

A further object or the present-invention is to provide an improved inexpensive -s'witch construction havin'g a "minimum number'dfpa'rts'that lends itself particularly "well t'o fast assembly iinder inass produ'ctio'n methods. v

Still -an'other object ofthe p'res'ent invention-is to -provide "a simple improved'tone control arrahgeinent especially useful insinall portable hearing apparatus.

The "features or the present "invention which are'believe'd to'be novelare 'st' forthwith particularityin the appended claims. Th iprese'nt invention itself, both as'to its organizationand nianner'of operationftogetl'ier with further ob- ;iects' andadvantages'thereof' niay best be understood by'reference to the following description taken in connection with accompanying drawings inwhich:

Figure-1 shows'an improved combination tone control and Ion-off switch incorporated ina hearing-aid-circuit in accordance with th present invention;

Figures 2 through'5 show certain'elements of M5 Figure 12 shows a sectional view taken substantially on line 22 m of Figure 1;

'Figurel3 is 'afside view partly in section taken ionfthe line"! 3 I 3 of Figure 1;

"Figure 14 is one modification of the present invention asincorporated in a rotating cylindrical switch and Figure'l5 is another modification of the present invention as incorporated ina sliding switch. I

In Figure 1 thereis'illustrated a hearing aid circuit incorporating an amplifier including electron discharge device I, a second amplifier including electron discharge device? and-an output stage including electron discharge device '3. The three amplifiers are connected in cascade to amplify signals from microphone 4 and impress "such ainplified'signals onsound reproducing device 5 in linearly amplified form. Aswitch 6, described in detail hereinafter, for effecting on-off operation and tone control is interconnected with the amplifier.

As seen in Figures 1, l2 and 13, switch 6 has a fixed element 7 fixedly mounted on a base -8 by means of a pair'of positioning lugs 9 and a mounting stud [0 which has one end threaded to receive'a "pair 'ofnuts 'H which in turn provide secure mounting'of studl'fl in the base 8. Located "at "a suitable angular distance from each other in'fixed element'ly are conta'ctsiZ, I3, [4, and 'l 5,'-'also shown in' Figures 2 to 5 inclusive.

Positive drive between a rotating resilient contact"meiriberl6 and "a rotating knob I! is provided by an insulated'pin l8 projecting from knob l1 and passing'throughthe blade E9 of resilient contact member it. {A rounded embossment 20 formed inone end ofthe blade 21 of member E6 cooperates with the 'suitably'spaced 'detent grooves 22/23g24fl25'a1id26 inthe fixed element 1 to positivelylocatethe blades 21, 28, '29, 30 and 3! of'the' resilientcontact member 16 in desired re-' lation with the contacts l2,= I3, M and I5 in the fixed element 1.

Insiilatedipin H3, in addition to providing the positive drive between the rotating resilientcontact'member l6 and the'rotating knob ll, also cooperates with an arcuate shaped opening 32 in the fixed element 1 to confine rotation of the re silient contact member; and the rotating knob lTwithin desired limits.

Asseen'in Figures 1, 12: and 13, a cam surface 33 =is for'med asa part of fixed element' 1. In the first positionof'the switch 6, as illustrated in Figures 2'a-nd 7, thebladeZT of resilient contact member 16 tOliChes-C0ntaCt-1l In the second position, as -illustrated in-"Figures 3 and 8, the

3 blade 21 touches contact l3 and the blade 28 touches contact I2. In the third position, as illustrated in Figures 1 and 6, the blade 21 touches contact I4, the blade 28 touches contact I3, and the blade 29 touches contact I2. In the fourth position, as illustrated in Figures 4 and 9, the blade 21 touches contact I5, the blade 28 touches contact I4, the blade 29 touches contact I3 and the blade 39 touches contact I2. In the fifth position, as illustrated in Figures and 10, the blade 28 touches contact I5, blade 29 does not touch contact I4 because it has suificient length to engage the cam surface 33 and thus be held out of engagement with contact I4, the blade 30 touches contact I3 and the blade 3I touches contact I2. The blades 21 and 28, being shorter in length than blade 29, pass by the cam surface 33 without being lifted thereby and consequently are allowed to touch contact !4 when they pass thereover. length than the blades 21 and 28, cooperates with the cam surface 33 to be lifted clear of contact l4 as illustrated in Figure 5. The blades 39 and 3I also have sufficient length to reach the cam surface 33 but are limited in their rotation by the H to the operator the operating position of movable element I1.

The described switch is arranged to provide not only on-oif action for the discharge devices I, 2 and 3 but also several changes in tone. The various circuits of the amplifier are arranged together with the switch as follows for that pur pose.

One terminal of filamentary cathode 31 is grounded and the other terminal is connected through filamentary cathode 38 to the positive terminal of source 43 of operating current therefor. Similarly one terminal of filamentary cathode 39 is grounded and the other terminal connected to positive terminal of source 49. The negative terminal of source 49 is connected to the contact 53 of switch 6 so that the negative terminal of source 43 is grounded through resilient contact member I6 and grounded contact I2 to make the amplifier operative in the second, third, fourth and fifth positions of the switch 6.

The input circuit of device I extends from its control electrode through microphone 4 to the grounded terminal of cathode 31, whereby alternating potentials produced by microphone 4 are impressed between cathode 31 and control electrode 4!. A grid leak resistance 42 is connected in shunt with microphone 4 to maintain control electrode 4! at proper operating potential with respect to cathode 31.

The output circuit of device I extends from its anode 43 through the serially connected load resistance 44 and bypassing condenser 45 to the grounded terminal of cathode 31. Space current for device I is provided by connection of a point between resistance 44 and condenser 45 to the positive terminal of a source 46 of operating potential, the negative terminal of source 46 being connected to ground through a relatively small biasing resistor 41 for device 3.

The screen electrode 48 of device I is main- The blade 29, however, having greater tained at a constant positive potential with respect to cathode 31 by connection of a bypassing condenser 49 between screen electrode 48 and the grounded terminal of cathode 31 and by connection of a resistance 50 between screen electrode 48 and the positive terminal of source 46.

The input circuit of device 2 extends from its control electrode 5|, to the movable tap 52 of a volume control resistance 53 of which one terminal is grounded and the other terminal connected through coupling condenser 54 to anode 43, whereby any desired part of the alternating potential across resistance 44 may be impressed between control electrode 5| and cathode 38 of device 2 for further amplification.

The output circuit of device 2 extends from its anode 55 through a load resistance 56 to the positive terminal of source 46 and from the negative terminal of that source through resistance 41, ground, and filament 31 to cathode 38. Amplified alternating potential from device 2 therefore appears across resistance 56.

The screen electrode 51 of device 2 is connected to ground by a bypassing condenser 58 and to the positive terminal of source 46 through a resistor 59 so that it is maintained at a constant positive potential with respect to cathode 38.

The input circuit of device 3 extends from its control electrode 60 through a resistance BI and biasing resistor 41 in series to ground. Coupling condenser 62 is connected between control electrode 60 of device 3 and anode 55 whereby the alternating potential across resistance 56 is impressed between control electrode 69 and cathode 39 of device 3 for further amplification.

The output circuit of device 3 extends from its anode 63 through the serially connected primary winding 64 of the transformer 65 and bypassing condenser 45 to the grounded terminal of cathode 39. Space current for device 3 is provided by connection of a point between primary winding 64 and condenser 45 to the positive terminal of the source 46 of operating potential.

The screen electrode 66 of device 3 is connected to ground by the bypassing condenser 45 and to the positive terminal of source 46 so that it is maintained at a constant positive potential with respect to cathode 39 and the signal potential across resistance 6| is amplified linearly by device 3 and appears across the secondary winding 61 of the transformer 65 which is connected to impress those voltages on the sound reproducing device 5.

In order to prevent any substantial alternating potential across the resistor 41, a bypass condenser 68 is connected from the positive terminal of source 46 to a point between resistors 6| and 41.

The tone of signals reproduced by sound reproducing device 5 is controlled by the switch which connects resistance 69 and capacitance 19 in the hearing aid circuit thus far described. For that purpose resistance 69 is connected between control electrode M and contact member M of switch 6 and capacitance 10 is connected between anode 43 and contact [5 of the switch. In general, the resistance 69, which may be connected by switch 6 in parallel circuit relationship to the piezoelectric microphone 4, serves to reduce the intensity of low frequency signal components, and the capacitance 1|] which may be connected by switch 6 between the electrode 43 and cathode 31 of discharge device I serves to reduce the intensity of high frequency signal components. For

this purpose, switch 6 serves to connect one terminal of resistance 69 to ground and also serves to connect one terminal of condenser 10 to ground. Different types of tone may be procluced according to the four tonal positions of the rotary resilient contact member l6 shown in Figures 1, 3, 4 and 5. That is, the resilient contact member I6 is of such shape that in its counter-clockwise movement contact member 16 assumes positions where-by: (1) as in Figure 3 neither the resistance 69 nor the capacitance H1 is connected in the circuit, and neither the high notes nor the low notes are affected, and (2) as in Figure 1 the resistance 69 alone is connected in the circuit and high frequencies only are suppressed, and (3) as in Figure 4 both resistance 69 and capacitance 19 are connected in the circuit, and both some of the high and some of the low frequencies are suppressed and (4) as in Figure 5 the capacitance alone is connected in the circuit and high frequencies only are suppressed.

A modification of the previously described switch is shown in Figure 14an exploded view of a cylindrical rotating switch. A rotating element H is shown without a finger-knob for sake of clarity. A fixed element 12, that may be fixedly mounted on a suitable base (not shown) by any conventional means, such as a mounting bolt passed through its mounting hole 13, coacts with element H. A cam surface 14 is formed as part of the fixed element 12. A set of resilient blades 75, formed as a part of rotating element H, coacts with a set of contacts 16 in the fixed element 12 to give the desired electrical connections.

A blade 11, one of the set of resilient blades 15, by reason of its length coacts with the cam surface 14 to be lifted clear of a contact 18 in much the same manner as blade 29 is lifted clear of contact I4 in the switch 6.

Another modification of the first described switch is shown in Figure 15. A sliding element 19 coacts with a fixed element 80. A cam surface 81 is formed as part of the fixed element 80. A set of resilient blades 82 formed as part of the sliding element 19 coacts with a set of contacts 83 in the fixed element 80 to give the desired electrical connections.

A blade 84, one of the set of resilient blades 82, by reason of its shape, coacts with the cam surface 8! to be lifted clear of contact l4 in the switch 6. The remaining blades of the set of resilient blades 82 have a U-shaped part 86 incorporated therein in a position that allows these blades to clear the cam surface 8| and therefore all such blades touch contact 85 as they pass thereover.

The cam surface 81, being located between the fixed contact 85 and the sliding element 19 results in a switch having short, stubby resilient blades 82 that furnish positive wiping action across the fixed contacts 83 and fulfills all requirements for a short and compact switch.

The rotating cylindrical switch shown in Figure 14 has long flexible blades ideally suited for operation with a knob of small diameter.

The switch 6, shown in Figures 1, 12 and 13, although somewhat similar in arrangement to the modification shown in Figure 14 has its resilient contact member I6 formed in such manner that all the blades can easily withstand the bending that they are normally subjected to and consequently this results in a durable switch.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

I claim:

1. An electrical switch comprising a pair of resilient movable contacts, a pair of fixed contacts disposed in the path of said movable contacts, and a cam disposed adjacent one of said fixed contacts, said cam being arranged to operate on only one of said movable contacts, whereby said one movable contact is prevented from engaging said one fixed contact.

2. A rotary switch comprising a rotatable member bearing a pair of movable resilient radial contacts, the radial length of one of said contacts being greater than that of the other of such contacts, a pair of fixed contacts disposed in the path of said radial contacts, and a cam disposed adjacent one of said fixed contacts and in the path of said one movable contact only, whereby said one movable contact is prevented from engaging said one fixed contact.

3. A rotary switch comprising a first cylindrical structure bearing a pair of movable resilient axial contacts, the axial length of one of said movable contacts being greater than that of the other of such contacts, a second cylindrical structure coaxial with said first structure and bearing a pair of fixed contacts arranged in the path of said movable contacts, and a cam disposed adjacent one of said fixed contacts and in the path of said one movable contact only, whereby said one movable contact is prevented from engaging said one fixed contact.

BYRON R. CRISWELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,675,683 Woofter July 3, 1928 1,900,236 Hall Mar. 7, 1933 2,393,184 Passow Jan. 15. 1946 

